The embodiments described herein relate generally to reluctance motors, and more specifically, to a reluctance motor configured for use in an electric vehicle. In response to availability issues and costs associated with rare earth metals, electric motors free of rare earth metals are being developed. An example of a type of motor free of rare earth metals that is being developed is a reluctance motor. However, reluctance motors typically develop less torque than surface-mounted permanent magnet (SPM) motors and interior permanent magnet (IPM) motors that include high-performance magnets, for example, neodymium magnets. When included within an electric vehicle, an electric motor that develops higher torque is desired. As referred to herein, an electric vehicle is a vehicle that derives at least a portion of its propulsive force from an electric motor. For example, electric vehicles include vehicles that rely solely on an energy storage device and electric motor for propulsion, hybrid vehicles that rely on an energy storage device and electric motor for propulsion and a fossil fuel based motor to aid propulsion and/or to charge the energy storage device, and/or any other type of vehicle that includes an electric motor.
The magnitude of reluctance torque in a reluctance motor is known to rely on a difference (|Ld−Lq|) between a d-axis inductance (Ld) and a q-axis inductance (Lq). The size and number of windings can be increased to raise the reluctance torque, but it is difficult to increase output to the desired level because of the greater d-axis inductance (Ld) and q-axis inductance (Lq). The reluctance torque can be effectively increased by reducing the magnetic resistance of the LqIq magnetic path, increasing the magnetic resistance of the LdId magnetic path, and increasing a saliency ratio (Ld/Lq).
FIG. 6 is a front view of a known reluctance motor 100. Reluctance motor 100 includes a stator core 102 that includes a plurality of teeth 103 and a plurality of slots 104 defined between adjacent teeth. Motor 100 also includes coils 105 wound and fitted into the slots 104 formed between the teeth 103. Motor 100 also includes a rotor core 107 having a plurality of arc-shaped slits 108 and a plurality of arc-shaped magnetic paths 109 formed between each slit 108. The plurality of arc-shaped slits 108 formed in the rotor core 107 function as flux barriers, which increase the magnetic resistance in magnetic path LqIq, reduce the q-axis inductance (Lq), and increase the saliency ratio.
However, when slits 108 are provided within the rotor core 107 to function as flux barriers, q-axis magnetic flux leakage occurs on an outer diameter side of the rotor core 107 which limits the amount the q-axis inductance (Lq) may be reduced. In order to suppress q-axis magnetic flux leakage and further increase the saliency ratio, a known reluctance motor includes a plurality of independent (e.g., segmented) flux barriers having a magnetic path formed between a plurality of slits to reduce the q-axis inductance (Lq).
However, the independently formed and segmented flux barriers may cause issues related to centrifugal force during high-speed rotation of the rotor and to rotor strength with respect to acceleration. The segmented flux barriers also increase manufacturing complexity (i.e., it is difficult to realize a workable structure).